On 2019-Feb-02, Tom Lane wrote:
> In any case I think it makes things simpler and clearer, which is
> worth a good deal.
Looking at the patch, I agree -- this is clearer than what was there
before.
> Another idea that I looked into is to not create RestrictInfos for
> derived indexqual clauses, with the hope that that would further
> reduce the added overhead for the commuted-clause case. However
> that crashed and burned when I found out that the extended-stats
> machinery punts when given a bare clause rather than a RestrictInfo.
> It could possibly be fixed to not do that, but it looks like the
> consequences would be extra lookups that'd probably cost more than
> we saved by omitting the RestrictInfo. Also, having RestrictInfos
> means that we can cache selectivity estimates across multiple
> calls. I'm not entirely sure how much that matters in this
> context, but it's probably not negligible.
Is it reasonable to give ext-stats the option to receive either a
"plain" clause or a RestrictInfo, and if the former have it construct
the RestrictInfo and return it? It seems a pity to waste effort to
cater for ext-stats, only to be used in the rare case where any
ext-stats actually exist ... most of the time, it'd be wasted effort.
--
Álvaro Herrera https://www.2ndQuadrant.com/
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